If you want a total copy of your whole system for the inevitable emergency, our pick is CrashPlan. For the files you're working on? Dropbox. But what about backups of projects too big for Dropbox (or not worth the upgrade cost), but not needing full-system images? That's where Arq wants to fit in.

Arq is a Mac-only tool that does just one thing: backs up folders on your system to S3, Amazon's popular and rock-solid data storage service. You pay $29 for Arq, but after that, it's rather cheap to keep a big hunk of data on Amazon: $.125/GB per month, or $.093/GB per month for "Reduced Redundancy Storage." Even though Dropbox recently upped its free space to 16 GB, with referrals, there's the jump to a $99/year plan after you stretch past that space. Arq might be just the thing if you need to stash some big stuff and have regular access to it.